man: document the new Type=exec type
    
    And while we are at it, let's rearrange and extend the Type=
    documentation a bit. Let's make it an itemized list, and let's add a
    paragraph explaining which type best to use.
    
    (cherry picked from commit 79905a246d645d21633f09f564b3672d5085a85c)
    
    Resolves: #1683334
    
    patch_name: 0194-man-document-the-new-Type-exec-type.patch
    present_in_specfile: true
    location_in_specfile: 194
    squash_commits: true